Surface finishing apparatus



April 14, 1942. B. F. FOWLER SURFACE FINISHING APPARATUS Flled Feb 12, 1938 5 Sheets-Sheet 1 .3 a w www k bk I'NVENTOR. .357??? 7- row; 7?

April 14, 1942. B. F. FOWLER SURFACE FINISHING APPARAT S 5 Sheets-Sheet 2 Filed Feb. 12, 1938 ATTORNEYS INVENTOR. BEE? FPO-W15]? fli? April 14, 1942. FOWLER 2,279,782

SURFACE FINISHING APPARATUS Filed Feb. 12, 1938 5 Sheets-Sheet s I," 2 I INVENTOR.

/3 BERT F POM/1E7? /6 6 BY flf (M ATTORNEYS April 1942- B. F. FOWLER SURFACE FINISHING APPARATUS Filed Feb. 12, 1938 5 Sheets-Sheet 4 INVENTOR. BERT F'FOWZEP /7 'I'TORNEYS April 1942- B. F. FOWLER SURFACE FINISHING APPARATUS Filed Feb. 12, 1958 5 Sheets-Sheet 5 1N VENTOR.

BERT FT'OWLEP ATTORNEYS Patented Apr. 14, 1942 UNITED STATES PATENT OFFICE SURFACE FINISHING APPARATUS Bert F. Fowler, South Bend, Ind.

Application February 12, 1938, Serial No. 190,254

14 Claims.

This invention relates to metal surface finishing and more particularly to improvements in portable sanding machines of the endless belt type.

In my co-pending United States patent application, Serial No. 139,406, filed April 28, 1937, which matured as Patent No. 2,199,069, April 30, 1940, I have described and claimed a portable belt sanding machine embodying certain improved features and the present application may be considered a continuation in part of my said co-pending patent application, containing some common subject matter and some new subject matter.

In the surface finishing of metal structures such as automobile bodies, preparatory to applying paint or other protective or decorative coating, prior to my invention, a large amount of hand filing, scraping, etc. has been required. Attempts have been made to provide power driven devices to accomplish the hand finishing operations but without substantial success. It is among the objects of my invention to provide a portable power driven machine which can effectively and economically prepare metal surfaces for painting, which is adapted to surface finish flat, concave or convex surfaces of complex form and which is always under the complete and accurate control of the operator.

Other objects of my invention are the provision of a sanding machine of the type described in which heating and belt friction is reduced to a minimum; the provision of a sanding machine which will not endanger the health of the operator and which includes effective dust and waste material collecting means which will operate on the hot particles of metal which are removed by high speed belt sanding operations; the provision of a belt sanding device in which sanding belts can be removed and replaced quickly with a minimum of effort; the provision of a belt sanding machine for high production operation in which the danger of burning of dust collecting bags is eliminated; the provision of an improved backing shoe for belt sanders or the like whereby a finer surface finish can be obtained; the provision of a high speed, high production metal finishing tool which is completely under the con-- trol of the operator at all times and which is adapted to operate economically and hold up under modern high speed continuous production conditions.

My improved sanding machines, as described and claimed herein, have been in use on the regular production line in the body plant of one of the large automobile manufacturers of this country. They have reduced the cost of metal finishing in this plant by very substantial amounts and have operated successfully for long periods of time in continuous production use. Practically all of the laborious hand filing operations on the bodies have been eliminated by the use of my machines, thus relieving the workmen of the arduous work previously required to give the desired surface finish on the body. It will, of course, be understood that although I have referred particularly herein to the adaptation of my improved sanding machine to the finishing of automobile bodies and the like, it may be used for numerous other purposes where a portable, efficient and extremely sensitive surface finishing machine is required. Its effectiveness is not limited to metal articles but it may be used on any material which is adapted to sanding, A major problem in industry where abrasive action is depended upon for the removal of material is that of occupational diseases of the worker caused by inhaling the dust and particles removed by the abrasive Figure 1 is a plan view, partly in section, of one embodiment of my improved sanding machine shown in position to sand a vertical surface, the driving and sanding belts being illustrated in their free running or idle positions.

Figure 2 is a view generally similar to Figure l but illustrating the driving and sanding belts in working position, the inner surface of the driving belt being in engagement with the shoe surface.

Figure 3 is an elevational view, partly in sec-' tion, taken from the operators position and i1- lustrating the machine shown in Figures 1, 2 and 6 and its adjustable supporting bail.

Figure 4 is an enlarged fragmentary. view of one embodiment of my improved resilient, hard surfaced abrasive belt backing shoe.

Figure 5 is a vertical cross-sectional view, similar to Figure 4, but illustrating a modified form of shoe having a hard surfaced friction or contact plate adapted for substantially universal movement relative to its supporting pins.

. Figure 6 is a fragmentary sectional view of the operator's handle for controlling the engagement of the belt with the rigid surface of the backing shoe and illustrating a spring belt tensioner and cam and lever arrangement for releasing the belt tension to permit abrasive belts to be changed.

Figure 7 is an enlarged cross-sectional view of one form of my spark arresting and dust collect: ing device showing the baffle means for preventing matted waste material from dropping back into the dust collecting fan.

Figure 8 is a plan view generally similar to Figure l but illustrating my sanding machine equipped with my improved resilient air cushion shoe.

Figure 9 is a view taken on line 9-9 of Figure Figure 10 is an enlarged cross-sectional view of my air cushion shoe assembly taken on line III--III of Figure 8.

Figure 11 is a view generally similar to Figure 10 taken on line I I-I I of Figure 8.

Figure 12 is a top elevation of the slotted shoe.

Figure 13 is a perspective view of the bottom of my improved air cushion shoe.

Referring. now to Figure 1, the illustrated embodiment of my invention includes a main frame and motor housing I having handle members 2 and 8 secured thereto at its opposite ends. The driving motor (which is seen in section in Fig. 3) includes a rotor 4 and shaft 5 which is connected by suitable gearing to drive the pulley shaft 8 on which is mounted the belt driving pulley I. The motor 3 may be of any suitable type. I preferably employ an alternating current motor of the high-cycle type in order to obtain the desired power and high belt speed and still retain portability of the apparatus.

The pivotally supported belt pulley 8 is mounted on a shaft 9 which is carried by one arm I0 01' a bell crank lever, which may be generally referred to as II and which is pivotally supported on the shaft-or pin I2 which in turn is carried by the main frame I of the machine, as is seen in Figures 3 and 6. The other end I2 of the bell crank lever extends generally parallel to the length of the frame, and when a spring belt tension device is used, as shown in Figure 6, rather than the air cylinder of the apparatus of Figures 1, 2 and 3, carries at its outer end a shaft I4 to which is secured a cam member I5. On the other end of the shaft I4 a handle I6 is mounted. An abutment plate member I1 is secured to the frame I, as is seen in Figure 6, and is adapted to co-act with the cam IE to swing the bell crank lever .II about its pivot shaft I2 to move the pulley 8 toward the pulley I when it is desired to compress the spring P to remove a wom abrasive belt and replace it with a new one.

In the machine of Figures 1, 2 and 3, in order to maintain the desired tension on the abrasive belt I8 and the supporting belt I9 I provide a fluid pressure actuated device comprising a cylinder 28 mounted on the frame I of the machine. This cylinder, as is shown in Figure 1, contains a piston 2| having a piston rod 22 extending out of the end of the cylinder 20 and adapted to engage the arm I 9 of the bell crank lever II. The cylinder 20 is connected, on the left hand side of the piston 2|, to a source of suitable fluid under pressure, such as compressed air, through a pipe or conduit 22 and a pressure regulating valve 24 (Fig. 2) may be provided accurately to adjust the pressure'effective against the piston 2|. By adjusting the fluid pressure the force exerted by the piston rod 22 against the crank arm Il may be controlled and thus the tension on the belts I8 and 19 may be regulated. It will be understood that when the air cylinder 20 is employed the lever I6 and associated parts shown in Figure 6 maybe omitted because it is only necessary to release the pressure in cylinder 20 to permit sanding belts to be changed.

A lever arm 25 is secured to the end of the arm I 0 of the bell crank II as by means of screws 28. This arm 28 extends lengthwise of the body of the machine and has a transversely extending handle portion 21 at its end. This handle 21 extends parallel and adjacent to the fixed handle 2 and is so positioned that the operator can grasp both the handle 2 and the handle 21 simultaneously. Movement of the handle 21 toward the handle 2' will cause the bell crank arm III to swing toward the handle 2 and will move the pulley 8 away from the pulley I, thus increasing the tension applied to the belts I8 and I9. The function and operation of this handle member 21 will be later described.

A driving belt idler pulley 28 is rotatably mounted at the end of a supporting arm 29 which may be pivotally secured to the frame I of themachine by the bolt 30. A spring 2I is secured at one end to the arm 29 and at its other end to the frame I of the machine. This spring is normally maintained in tension and exerts a force tending to move the pulley 28 and the driving belt I9 inwardly toward the common center line of the pulleys I and 8. As is fully described in my above noted co-pending patent application, the provision of the idler pulley 28 permits the separation of the driving belt I9 from the abrasive belt I8 during the entire length of one run between the supporting pulleys, thus greatly increasing the cooling of the belts and giving greater pulley contact between the driving belt I9 and the driving pulley I.

A bracket 82 is secured to the main frame I by bolts 22. This bracket carries one form of my improved resilient shoe member (generally indicated at S) which forms the backing for the abrasive belt, and also supports the arms 24 and 38 which carry the auxiliary supporting rollers 26 and 31. respectively.

The shoe S includes a resilient body portion 38, preferably of sponge rubber or other material havlng generally similar resilient properties.

This sponge rubber is preferably mounted between the metal plate members 29 and 40. Guide pins and 42 extend through suitable apertures in the bracket 22, the plates 29 and 48, and the resilient body 28 and are adapted to have free movement therein. These pins H and 42 have threaded connections at their upper ends with the hard surfaced shoe or plate member 42, said shoe member preferably having spacer boss portions 44 which maintain it in spaced relation to the top plate 48 which covers the resilient body 38. The lower ends of the pins M and 42 are provided with enlarged heads 45 and 48 to limit the upward movement thereof and thus restrict the upward movement of the hard surfaced shoe or plate 42. From the above description it will be seen that the belts I8 and I8 may have what may be termed substantially universal movement due to .variations in pressure of the belt I8 againstthe'work while the pins H and 42 prevent lateral displacement of the plate 43 and the entire shoe assembly 8, due to the frictional engagement of the belt I! on the plate 43. By providing an air space between the plate 43 and the body 33 of resilient material the transfer of heat to the resilient body 38 is greatly reduced and its life correspondingly increased.

It will be seen that pressure against the belt I. adjacent one end of the shoe plate 43 may cause the same to be depressed, compressing the resilient body 33, without substantial downward movement of the other end of the plate 43. A substantially universal tilting-action may also be given the plate 43 and this is one of the features of my invention which permits it to be successfully used in fine metal surface finishing. particularly on thin sheet metal where excessive pressure at any one point such as might be caused by relatively rigidly mounted shoes might result in wearing completely through the metal.

As is clearly seen in Figures 1 and 2 the plate 43 and the resilient member 33 are adapted to hold the belts It and is out of their normal straight line path between the pulleys 1 and 3 so that the working surface of the sanding belt is projects out away from the rest of the machine thus greatly facilitating the application of the belt to concave and convex surfaces and making possible the desired sensitive resiliency which is imparted to the working surface of the abrasive belt by my improved belt backing shoe and support arrangement.

Auxiliary belt supporting rollers 33 and 31 are disposed at the opposite ends of the shoe 8. The arms 34 and 35 which carry these rollers are pivotally mounted on pins 41 and 4B which are carried by the bracket 32. Lugs 43 and 33 on the bracket 32 form abutments for the screws II and 32 which co-act with the lugs to form adjustable stops for the arms 34 and 33 limiting the movement thereof in a direction towards the shoe 8. Springs 53 and 54 are secured respectively to the arms 34 and 35 and to a flange 55 on the bracket 32. These springs normally hold the arms 34 and 35 and the rollers 33 and 31 in the position shown in Figure 1. As is seen, the screws II and 52 are preferably adjusted so that the inner surface of the belt is clears the surface of the friction shoe 43 and is com pletely out of contact therewith. Lock nuts ii and 52' are adapted to hold these screws in adjusted position. The air pressure on the cylinder 20 is adjusted so that it does not overcome the springs 53 and 54 or the spring 3| to move the belts out of the position shown in Figure 1.

It will be seen that when the parts are as shown in Figure 1 the belts l3 and It will run freely with a. minimiun of friction or rubbing contact with other parts of the apparatus. The driving belt l8 contacts only the main pulleys 1 and I and the idlers 28, 36 and 31 and thus very little heat is generated although the motor may be driving the belt at its full speed.

When the operator desires to apply the working surface of the belt l3, 1. e., that part which lies between the pulleys 36 and 31, to the surface to be finished he squeezes together the handles 2 and 21. This causes the pulley 8 to move away from the pulley 1, the bell crank arm ll swinging about its pivot 12. The arms 34 and 35 will move about their pivots. lowering the rollers 33 and 31 relative to the surface of the plate 43 and permitting the belt l9 to bear against the plate 43 (see Fig. 2). when in this position the resilient backing action of the shoe 5 will be effective and the desired control of the contact of the sanding belt with the surface can be obtained. When the operator removes the belt from the work to change its position, or for an other reason, and he does not desire to shut off the driving motor by manipulation of the hand operated motor switch control 8|. he simply releases his grip on the handles 21 and 2, permitting the springs 33 and 34 to return the idler pulleys II and 31 to the positions shown in Figure 1 and again moving the inner surface of the driving belt II away from and entirely clear of the surface of the plate 43. Furthermore, by varying the degree of pressure exerted on the handle 21 the belt I! may be caused to contact with the shoe surface with more or less pressure thus giving the operator a very sensitive means for controlling the abrasive action of the sanding belt which is carried by the driving belt. As will be understood the belt I I is relatively heavy while the sanding belts are relatively light and are discarded after their abrasive surface is worn out.

Electrical connections to the driving motor may be provided through the conduit 51 and a guard plate 53 is adapted to cover the length of the sanding belt on the side opposite its workin surface. provided and is preferably adapted to swing back out of the way about a pivot 63 to facilitate replacement of the sanding belts.

As shown in Figure 3, bracket members SI and 82 are secured to the main frame I and have pivotal connections at their ends to the bail member 83. A supporting pulley 64 is carried by a bracket 65 which may be supported from the ceiling and counterwelghted to balance the weight of the sanding machine in well known manner. Adjustable stops 36 and 61 can be clamped on to the ball at any desired points to limit the possible degree of tilting of the sander. The pivotal supports at the ends of the bail and the bracket 3| and permit rota- I tion of the sander to accommodate and follow any surface contour. By properly counterbalancing the machine the operator's only efiort is that involved in guiding the belt over the surface to be finished and controlling the belt tension by the handle 21.

'In Figure 5 I have illustrated a modified form of backing shoe in which a resilient body 38 corresponds to the body 38 of Figure 4. Pins 69 and 10 extend through the body 68 and are adapted for free movement therethrough. At the bottom of each of these pins there is a washer 1| and cotter pin 12 which limit the movement thereof. The upper ends of the pins are ball shaped and fit into corresponding sockets in the members 13 on the friction plate 14. The ball and socket joints thus provided permit the plate 14 to tilt either longitudinally or laterally relative to the resilient body 68. This arrangement permits the surface of the sanding belt to follow the surface being finished with a minimum of tendency A hinged curved end guard 53 is also In Figures 9 and 10 a sanding machine is illustrated which is substantially the same as that shown in Figures 1 and 2 except that my improved air cushion belt backing shoe has been employed and a slightly different arrangement of the spark arrester is utilized. Similar parts are indicated by the same reference characters as used in describing Figures 1 and 2 and reference will be made here primarily to the different features of the apparatus.

An air cylinder 05 performs the same function as the air cylinder 20 in Figures 1 and 2. Air is supplied to the cylinder 05 through a pipe and a T 01 which directs a part of the air to the cylinder 00 and a part to the conduit 00, preferably a flexible rubber hose or the like. This hose 00 extends to the shoe 8' which is shown in detail in Figures 10, 11, 12 and 13.

Figure 10 is a cross-sectional view taken substantially on line I 0I0 of Figure 8. The shoe supporting bracket 99 is secured to the main frame of the machine by screws 33 and has bosses I00 formed thereon through which the guiding and supporting pins IOI extend. These pins IOI are free to move in the holes in the bracket 99 and extend through spacing washers I02 at their upper ends and have threaded engagement with the grooved shoe member I00. The resilient sponge rubber shoe backing I00 has top and bottom plates I and I00- which are preferably of fiber or other substance which tends to resist the transfer of heat. The pins IOI are allowed to move freely through the block I00 and plates I05 and I00 and coil springs I01 are disposed around each pin IOI between the supporting bracket 09 and the bottom plate I00. These springs coact with the sponge rubber block I 00 to provide a very effective resilient and substantially universal support for the driving belt I0 and the sanding belt I0.

The shoe I03 has a plurality of elongated narrow grooves I00 cut in its outer surface, as is clearly seen in Figures 10, 11 and 12. The air p'pe or tube 98 connects to a short connecting tube I09 which is threaded into a transversely extending rib IIO on the bottom of the shoe I03. This rib I I0 is preferably of the same thickness as the spacing washers I02 so that the shoe I03 is held in spaced heat insulating relation to the top plate I00 of the sponge rubber block assembly. A hole III, which may be formed by drilling transversely through the rib H0 and then plugging the ends as indicated at I I2, forms an air passagewhich connects with the tubes I09 and 00 and each of the grooves I00 is cut sufllciently deep into the surface of the shoe I03 that it intersects the transverse hole III.

When the machine is operating the belts travel in the direction shown by the arrow in Figure 8 and. as air under pressure is supplied to the pipe 00 to operate the belt tensioning cylinder 05, air under pressure also will pass through the pipes 00 and I09 to the transverse passage III which will distribute the airinto each of the narrow longitudinally extending grooves I00. A valve (not shown) may be inserted in the hose or pipe 00 to regulate the quantity of air discharged into the grooves I00. As is seen in Figure 12 the grooves I00 stop short of the ends of the shoe I00 and the belt I0, as it runs up on the shoe I00, forms a resistance to the escape of the air from the right hand .end of the grooves in the shoe I00 (as seen inFig. 8). The grooves I00 also stop short of the sides of the shoe I00 leaving a smooth belt engaging portion I I0 on each side. In operation, the

catching apparatus.

tendency is for the air to be maintained under pressure in the elongated grooves I00 and to form a cushion support for the belts l0 and II. This action has proved to be very effective in obtaining the finest quality of metal finishing. It has been found that by using my improved air cushion shoe construction with a sanding belt of approximately No. 30 grit a finish can be obtained which has the appearance of one made by a No. grit belt used on a shoe without the air cushion feature. This permits coarser belts to be used while still obtaining the desired fineness of surface finish. The air which passes into the grooves I 00 and escapes out all. around the edges of the shoe I00 also greatly assists in cooling of the shoe and belts and, when combined with my improved manual means for causing the belt to engage the shoe only during actual sanding operations, results in a device which has a sensitivity of touch or feel whereby an extremely high quality of work can be done. Although longitudinal grooves I00 have been illustrated it will be understood that the shoe surface may be provided with other forms of elevated and depressed portions without departing from the spirit of my invention. 7

In order to protect the operator from the harmful effects of the metal dust and particles of abrasive thrown off when my sanding machine is in operation, I have incorporated in the illustrated embodiment thereof a suction fan I0 adapted to be driven by a separate motor I6 which if desired may be connected to a separate source of current through conductors 11. The suction inlet to the fan I5 includes two passages, one of which, I0, has an opening which is generally parallel to the working face of the sanding belt and which is provided with a flexible mouthpiece or scoop I0, of rubber or the like, which extends out beyond the line of travel of the working surface of the belt I0. A metal wear plate I0 protects the scoop I0 from abrasive wear and. being resilient, permits the scoop to be deflected if it should strike against the work. When the machine is operating the belt rotates in the direction indicated by the arrow in Figure 1 and a large part of the sparks immediately picked up by the scoop-shaped mouthpiece I9 and are sucked down through the passage I0 by the action of the suction fan I5.

Some of the particles of removed metal and abrasive, however, may adhere to the belt and travel around the pulley]. In order to catch these a second preferably Venturi-shaped suction passage 00 is provided in the housing of the dust This collects the remaining particles which were not caught and conductedthrough the passage 10. Both the passages I0 and 00 open into the fan housing 15- which is provided with a discharge outlet 0I. It will be understood that any type of fan or blower may be employed so long as the suction inlet is connected to the passages I8 and 00 and a suitable outlet is provided.

In order to prevent distribution of the collected particles of material back into the atmosphere it is necessary to provide a bag or the like which will collect the solid materials but which will permit the air draft to pass therethrough so that the desired suction may be maintained at the openings of the passages I0 and 00. As the high speed operation of this machine results in particles of red or white hot metal being drawn'through the suction fan and blown out through the opening 0|,

a serious problem is encountered to prevent setting the fabric bags 82 on fire. These bags 82 are necessarily made of a material which will prevent the passage of solid material but will not unduly restrict the passage of air therethrough. I have completely overcome the fire hazard by providing a tubular, perforated, generally cylindrical member 83 which is secured to a sleeve 84 which in turn fits over the enlarged outlet member 85. Preferably the member 83 is made of sheet metal containing closely spaced holes, for example, sheet brass having holes approximately Jr" in diameter spaced on about y centers although the specific arrangement and construction may be varied as shown in Figures 8 and 9. .Walls of this kind effectively stop and cool the white hot particles of metal, etc. before they can come into contact with the bag 82. As the operation of my sanding machine results in the formation of very fine elongated shavings of the metal whichis being surfaced these shavings tend to mat together in the tubular member 83 and form a ball. In order to prevent this ball from rolling back into the fan plate 15 when the machine is tilted in such a direction as to cause the ball to move towards the fan plates, I have provided a baffle 88 which extends across the tubular perforated shell 83 and which will permit the particles of material to pass into the spark arrester and shaving collector 83 but which will prevent the ball of matted material from rolling back into the fan. The end of the tubular perforated member 83 is preferably closed by a door 81, of perforated metal asillustrated in Figure '7, if desired, or solid as shown in Figure 8, l

which may be hinged at 88 and is provided with a spring latch 89. This facilitates the emptying of the spark arrester after a period of operation of the machine sufficient to collect a substantial mass of material therein. My dust collecting means is very compact and does not interfere with the complete portability of the sanding machine. The spark arrester I I5 which is shown in Figures 8 and 9 is slightly modified from the one illustrated in Figures 1 and 2 in that it is mounted on the fan outlet at a slightly different angle and is provided with a solid end piece H6 which may be desirable in some classes of work.

When it is desired to change sanding belts the air pressure applied through the pipe 23 (Figs. 1 and 2) may be shut off from the cylinder 20 thus permitting the bell crank arm l and pulley 8 to move toward pulley l loosening the belt I8 so that it can be easily removed and replaced. When the spring belt tension device of Figure 6 is used the lever handle I6 is thrown to the right causing the cam l to engage the surface I'I thus swinging the hell crank Ii about its pivot and causing the arm I0 thereof to move to the left carrying with it the pulley B. The cam I5 is so shaped that it will maintain the bell crank II in the released position until the operator throws the handle l6 back to the position shown in Figure 6 and thus greatly facilitates the removal of a worn sanding belt and its replacement witha new one.

As will be seen from the above description of h the illustrated embodiments of my invention I have provided a portable metal finishing unit in which a high speed abrasive belt is employed and means are provided for effectively preventing the distribution into the air of the particles removed by its action. In my machine friction and finished, and an extremely resilient and substantially universal flexible support or backing for the abrasive belt is provided whereby .surfaces can readily be followed without danger of gouging, cutting or undesired removal of material by the sanding belt. Heating of the backing shoe and of the driving and abrasive belts is greatly reduced. In using my improved type of abrasive shoe in which a resilient body such as sponge rubber is employed the elimination of heat is of considerable importance because heat causes the sponge rubber body to deteriorate and lose its flexibility. By providing my improved control handle and lever arrangement whereby the belt engages the shoe only during actual work the heating of the shoe is greatly reduced and thus the life and effectiveness correspondingly increased. A very fine surface finish can be obtained with my machine and the use of coarser sanding belts will produce a surface equal to that produced by much finer belts used with other types of equipment. The air cushion shoe assists in cooling the belts and gives a floating backing for the belt which has been found to be very effective in obtaining the finest possible surface finish.

Although I have described the illustrated embodiments of my invention in considerable detail it will be understood by those skilled in the art that modifications and variations may be made in the specific forms which I have shown and described without departing from the spirit of my invention, and I do not, therefore, wish to be limited to the particular apparatus illustrated and described herein but claim as my invention all embodiments thereof coming within the scope of the appended claims.

I claim:

1. In apparatus of the type described, a frame, a handle on said frame, spaced pulleys supported by said frame for relative movement toward and away v from each other, a belt carried on said pulleys, means for exerting a predetermined force tending to move said pulleys apart and independent manually operable means for increasing the force tending to move said pulleys apart from said predetermined value and increasing the spacing between said pulleys, said manually operable means including an operating lever having a handle portion disposed adjacent said handle on said frame. v

2. In apparatus of the type described, a frame, spaced pulleys supported by said frame, one of said pulleys being movable toward and away from the other, an endless belt encompassing said pulleys, fluid pressure actuated means for moving said movable pulley away from the other pulley to apply tension to said belt, and independent manually operable means for increasing the tension applied to said belt by said fiuid pressure actuated means and for releasing such increased tension.

3. In apparatus of the type described, a frame, spaced pulleys supported by said frame, one of said pulleys being movable toward and away from the other, an endless belt encompassing said pulleys, a shoe member adapted to engage the inner surface of said belt between said pulleys, resilient means for applying tension to said belt, resilient means for normally holding said belt out of frictional engagement with said shoe, and manually operable means for increasing the tension applied to said belt to move said belt into engagement with said shoe.

4. In apparatus of the type described, an endless belt, spaced pulleys for supporting said belt, means for driving one of said pulleys to operate said belt, a shoe memberadapted to engage and support the innei' side of said belt, means for normally maintaining said belt out of contact I with said shoe while operating, and means operable while said belt is operating to'move said belt into and out of contact with said shoe.

pulleys'apart and exert a tension on said belt,

and a lever secured'to said arm and manually operable to move 'said pulleys farther apart than the positions they assume'under the influence of Isayiresilient means.

6. In apparatus of the type described, a frame,

in spaced pulleys supported by said frame, one of said pulleys being movable toward and away .from the other, a belt encircling said pulleys, a

shoe'member adapted to engage the inner surface of said belt, resilient means exerting a force .tendingto move said movable pulley away from the other pulley, resilient auxiliary belt supports adjacent the ends of said shoe for normally holding said beltout of contact with said shoe, and manually operable means for exerting an additional force to move said movable pulley and cause said belt to move said resilient supports and come into contact with said shoe, said resilient supports being adapted, upon release of said manually operable means, to return said belt to out of contact relation with said shoe.

7. In a sanding machine of the type-described, a frame, spaced pulleys supported by said frame, one of said pulleys being movable toward and away from the other, a belt encircling said pulleys, means for exerting a force tending to move said frame and supporting said belt, means for driving one of said pulleys, a shoe having a grooved face disposed adjacent and substantially covered by the inner surface of said belt, the grooves in said face extending in the direction of belt travel from a point adjacent one end of said shoe to a point adjacent the other end of said shoe-and means for discharging fluid under pressubstantially covered by the inner surface of said belt, and means for discharging air into' said grooves while said belt is being driven.

11. In apparatus of the type described, a belt, means for driving said belt, a shoe having a belt engaging surface provided with raised and depressed portions, said depressed portions stopping short of the edges of said belt engaging surface and extending for substantially the full length of said shoe, means for supporting said shoe in belt backing-up position and means for discharging fluid under pressure into said depressed portions of said shoesurface whereby the fluid under pressure flows through said depressed portions in the said pulleys apart, means for driving one of said pulleys, a guiding and supporting handle on said frame, means, including an operating handle disposed adiacentsaid guiding handl and adapted to be grasped therewith, for moving said movable pulley away from the other of said pulleys, and spring means whereby said movable pulley will be moved toward said other pulley upon release of said operating handle.

8. In a sanding machine of the type described, a frame, spaced pulleys supported by said frame, one of said pulleys being movable toward and away from the other, a belt encircling said pulleys, means for driving one of said pulleys, a backing shoe for said belt, a guiding and supporting handle on said frame, means, including an operating handle disposed adjacent-said guidinghandle and adapted to be grasped therewith, for moving said movable pulley away from the other of said pulleys, and spring means whereby said movable pulley will be moved toward said other pulley upon release of said operating handle, said last named means including an arm carrying a roller engaging said belt and bein direction of belt travel for substantially the full length of said shoe.

12. In apparatus of the type described, a frame, spaced pulleys carried by said frame, a belt encircling said pulleys, means for driving one of said pulleys and a shoe carried by said frame and adapted to back up and support said belt between said pulleys, said shoe including a resilient supporting portion and a rigid belt engaging plate carried by said supporting portion, said plate having a grooved belt engaging surface, and means for discharging 'air between said belt and plate surface.

13. In apparatus of the type described, a frame, an endless belt, means carried by said frame for supporting and driving said belt and a belt backing shoe supported by said frame, said shoe including a body of resilient material mounted on said frame, a guide pin adapted to have limited free movement toward and away from said belt, a belt engaging plate having a grooved belt engaging surface'and being secured to said pin and disposed between said belt and said resilient body, and means for directing air under pressure between said belt and grooved surface.

'14. In combination in a portable surface flnishing machine of the class described, a surface finishing belt, means for supporting and driving said belt, a backing member for said belt having a substantially plane face elongated in the direction of belt movement, a plurality of grooves in said face extending substantially parallel to the direction of belt movement and stopping short of each end of said face, and means for discharging a r thereof.

BERT F. FOWLER.

under pressure into said grooves at one end 

